U.S. patent number 7,059,404 [Application Number 10/424,309] was granted by the patent office on 2006-06-13 for variable intensity memory gravel pack imaging apparatus and method.
This patent grant is currently assigned to Core Laboratories L.P.. Invention is credited to Michael J. Flecker, J. Thomas Hampton, III, Larry Stephenson.
United States Patent |
7,059,404 |
Flecker , et al. |
June 13, 2006 |
Variable intensity memory gravel pack imaging apparatus and
method
Abstract
An apparatus and method are provided for varying an operating
parameter for a nuclear gamma ray tool for evaluating the integrity
of gravel packing. The gamma ray outpat intensity and area of
investigation are altered by changing a source housing geometry and
the material from which the source housing is made. An actuator is
provided to slide a variable electron density sleeve over the
source and to vary the area of investigation by changing the
distance between the source and a detector.
Inventors: |
Flecker; Michael J. (Sugarland,
TX), Stephenson; Larry (Kennedale, TX), Hampton, III; J.
Thomas (Houston, TX) |
Assignee: |
Core Laboratories L.P.
(Houston, TX)
|
Family
ID: |
31188762 |
Appl.
No.: |
10/424,309 |
Filed: |
April 28, 2003 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040020646 A1 |
Feb 5, 2004 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
09447393 |
Apr 29, 2003 |
6554065 |
|
|
|
Current U.S.
Class: |
166/250.02;
166/253.1; 166/254.2; 166/278; 166/66; 175/41; 250/269.1; 378/198;
73/152.14 |
Current CPC
Class: |
E21B
43/04 (20130101); E21B 47/00 (20130101); G01V
5/125 (20130101) |
Current International
Class: |
E21B
43/04 (20060101); E21B 47/00 (20060101); G01V
5/04 (20060101) |
Field of
Search: |
;166/247,250.01,255.1,250.02,253.1,254.1,254.2,278,51,65.1,66
;175/40,41 ;324/323-369 ;376/160-166,108-119,191
;378/44,45,46,49,50,70,86,88,89,197,198 ;73/152.14,152.54
;250/269.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
CoreLab, Imaging-PackScan(TM) Gravel Pack Density Imager, Nov. 4,
2002, 5 pages. cited by examiner .
CoreLab, Imaging-PackScan(TM) Gravel Pack Density Imager, Aug. 19,
2002, 6 pages. cited by examiner .
CoreLab, Imaging-Washpipe Conveyed SpectraScan Imaging, Jan. 2005,
2 pages. cited by examiner .
CoreLab, Imaging-PackScan(TM) Gravel Pack Density Imager, Jan.
2005, 2 pages. cited by examiner .
CoreLab, Imaging-SpectraScan Imaging, Jan. 2005, 2 pages. cited by
examiner .
CoreLab, Imaging-Completion Profiler, Jan. 2005, 3 pages. cited by
examiner .
S.S. Sollee; Gravel-Pack Logging Experiments, 60.sup.th Annual
Technical Conference and Exhibition of the Society of Petroleum
Engineers, Sep. 22-25, 1985, SPE 14163, pp. 1-10. cited by
other.
|
Primary Examiner: Gay; Jennifer H.
Attorney, Agent or Firm: Madan, Mossman & Sriram,
P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This patent application is a continuation-in-part of and takes
priority from U.S. patent application Ser. No. 09/447,393 filed on
Nov. 22, 1999 entitled "Memory Gravel Pack Imaging Apparatus and
Method" (U.S. Pat. No. 6,554,065, issuing on Apr. 29, 2003).
Claims
What is claimed is:
1. A method of varying output radiation for a nuclear source for
evaluating degree of gravel pack in a predefined annulus between a
tubing and wellbore inside, comprising: providing a downhole tool
housing the nuclear source, said tool adapted to sense data in said
tool corresponding to nuclear energy received by at least one (1)
detector carried by said tool in response to nuclear energy
generated by the nuclear source; varying output radiation intensity
for the nuclear source; and varying an electron density for a
source housing surrounding the nuclear source.
2. The method of claim 1 wherein varying the election density for
the source housing further comprises: varying a thickness for the
source housing surrounding the nuclear source.
3. The method of claim 1 wherein varying the electron density for
the source housing further comprises: sliding a sleeve made of a
material having an electron density over the nuclear source to
alter the gamma ray intensity output from the source housing.
4. The method of claim 1, further comprising: providing a borehole
eliminator between the source and the detector to prevent gamma
rays from traveling directly from the nuclear source to the
detector thereby enabling the tool to operate in larger diameter
boreholes.
5. The method of claim 1 wherein varying the election density for
the nuclear source further comprises: sliding a sleeve made of a
material having a variable electron density over the nuclear source
to alter the gamma ray intensity output from the source
housing.
6. The method of claim 1, further comprising: conveying said tool
by a conveying member selected from a group consisting of a (i)wash
pipe; (ii) slickline; (iii) electric wireline; and (iv)
coiled-tubing.
7. A method of varying output radiation for a nuclear source for
evaluating degree of gravel pack in a predefined annulus between a
tubing and wellbore inside, comprising: providing a downhole tool
housing the nuclear source, said tool adapted to sense data in said
tool corresponding to nuclear energy received by at least one
detector carried by said tool in response to nuclear energy
generated by the nuclear source; varying output radiation intensity
for the nuclear source; and varying an electron density for a
source housing surrounding the nuclear source wherein varying the
election density for the source housing further comprises varying a
material from which the source housing is made.
8. A method of varying output radiation for a nuclear source for
evaluating degree of gravel pack in a predefined annulus between a
tubing and wellbore inside, comprising: providing a downhole tool
housing the nuclear source, said tool adapted to sense data in said
tool corresponding to nuclear energy received by at least one (1)
detector carried by said tool in response to nuclear energy
generated by the nuclear source; and varying an area of
investigation for the tool by changing a source housing from a
first housing having a first dimension between the source and
detector to a second housing having a second dimension between the
source and detector.
9. A method of varying output radiation for a nuclear source for
evaluating degree of gravel pack in a predefined annulus between a
tubing and wellbore inside, comprising: providing a downhole tool
housing the nuclear source, said tool adapted to sense data in said
tool corresponding to nuclear energy received by at least one
detector carried by said tool in response to nuclear energy
generated by the nuclear source; and varying an area of
investigation for the tool by moving the source along a
longitudinal axis thereby varying a distance between the nuclear
source and detector.
10. An apparatus for evaluating degree of gravel pack in a
predefined annulus between a tubing and wellbore, comprising: a
conveying member adapted to be dispose in the wellbore; a nuclear
source positioned on the conveying member; a housing surrounding
the nuclear source and varying the output radiation of the nuclear
source; and a downhole tool at an end of the conveying member, said
tool adapted to sense data corresponding to nuclear energy received
by at least one detector carried by said tool in response to
nuclear energy generated by the nuclear source.
11. The apparatus of claim 10 further comprising: a plurality of
source housings having a variable electron density.
12. The apparatus of claim 11 further comprising: a plurality of
materials having different electron densities from which the
plurality of source housings are made.
13. The apparatus of claim 11 wherein the plurality of source
housings each have a different thickness for varying the output
intensity from the plurality of source housings.
14. The apparatus of claim 11 further comprising: a movable sleeve
made of a material having an electron density over the nuclear
source; and an actuator to slide the sleeve over the source to
alter the gamma ray intensity output from the source housing.
15. The apparatus of claim 10, further comprising: a borehole
eliminator placed between the nuclear source and the detector.
16. The apparatus of claim 10 further comprising: a plurality of
source housings for varying an area of investigation for the tool
by changing a source housing from a first housing having a first
thickness between the source and detector to a second housing
having a second thickness between the source and detector.
17. The apparatus of claim 10, further comprising: an actuator for
varying an area of investigation for the tool by moving the source
along a longitudinal axis thereby varying the distance between the
source and detector.
18. The apparatus of claim 10 further comprising: an actuator for
sliding a sleeve made of a material having a variable electron
density over the nuclear source to alter the gamma ray intensity
output from the source housing.
19. The apparatus of claim 10, wherein said conveying member
includes at least one of a member from a group consisting of a (i)
wash pipe; (ii) slick line; (iii) electric wireline; and (iv)
wiled-tubing.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to well logging tools and methods, and more
particularly to a memory logging tool having a variable output
radiation field intensity and variable area of the investigation
for evaluating the degree of gravel packing.
2. Description of the Related Art
A vast array of tools are utilized to log oilfield wells during
drilling and completion, and production phase of such wells. These
logging tools obtain measurements relating to the drilling
operation, wellbore condition and characteristics of the formation
surrounding the wellbore. After drilling the wellbore to a desired
depth, and before allowing it to produce hydrocarbons from a
hydrocarbon-containing subsurface formation, the wellbore is made
ready or "completed."
The completion operations usually include, among other things,
lining the wellbore with a casing made of jointed metal tubulars,
filling the annulus between the casing and the well with cement,
installing sand screens, and perforating the casing and the
formation at selected depths across from the hydrocarbon-containing
strata to allow the hydrocarbons to flow from the formation to the
wellbore. The formation fluid flows from the formation into the
well via the perforations because the formation pressure is greater
than the pressure in the well.
The free flow of the formation fluid into the well causes sand in
the formation to flow into the well at relatively high flow rates,
which can erode the tubular and other equipment in the wellbore.
Such other equipment includes flow control valves, sensors, safety
devices usually installed in the well to control fluid production
through the well and for safety reasons.
One or more metallic screens, usually referred to as sand control
screens, are placed in the wellbore to prevent inflow of formation
solid particles (fines). Gravel is packed between the formation or
casing and the production tubing to inhibit sand flow into the
production tubing. Proper gravel packing is a critical step in the
completion of a well.
Numerous gravel packing methods or procedures have been developed
to inject sand or proppant into the annulus between the permeable
screen and the production tubing in high permeability formations.
As noted above, the annular sand pack performs the function of
filtering formation solid particles which migrate into the well so
that they cannot plug or limit production and to eliminate the
erosion effects of the produced sand, which can damage the wellbore
equipment, and in extreme cases cause the loss of the well. These
procedures are referred to in the oil and gas industry as Gravel
Pack, Frac Pack, Water Pack, etc., each of which is designed to
provide essentially the same function--to completely and tightly
fill the screen/casing annulus with sand or poppant with no voids
or partially packed intervals. The gravel pack depth can range from
a few (10) to several thousand (1000 5000) feet. The gravel pack
acts as a filter that prevents the entry of formation fines into
the wellbore without restricting the flow of the formation fluids.
It is thus important to determine the integrity of the gravel pack.
The success of the gravel pack and the longevity of the wellbore
depends upon the extent and continuity of the gravel pack within
the annulus.
The effectiveness of gravel placement in the screen-casing annulus
or behind the casing (such as when prepacking perforation tunnels)
is normally evaluated with treatment-pressure data. Darcy's law,
volumetric calculations along with treatment pressure evaluation
and pressure testing methods are used to estimate the level of
gravel fill, with the minimum requirement being that the sand level
must extend into the blank pipe above the top of the screen. This
allows for the potential future settling of the sand. A direct
measurement locating the top of the gravel pack and the quality or
continuity of the sand fill within the annulus is preferred. Such
measurements can be utilized to improve the above-noted treatment
pressure data derived estimates. The continuity or absence of
significant voids within the packed annulus is best evaluated with
a direct measurement. Locating the voids soon after the completion
is important because such voids can not normally be detected with
the pressure evaluation methods. Voids can require workover of the
gravel pack, and in extreme cases, can even lead to complete
failure of the well.
At present, voids in the gravel-packed screen-casing annulus are
usually evaluated from data from density, neutron, gamma-tracer or
pulsed-neutron logs. These logs are usually obtained by wireline
logging tools, which require a separate trip into the well and are
often not performed promptly after finishing gravel packing. Also,
when radioactive materials are used for evaluating proppant
placement, gamma measurements are affected by the background
signals produced by such radioactive materials. These background
signals make the conventional density and pulsed-neutron
silicon-activation methods relatively ineffective.
The ability to alter output radiation intensity from a source sub
is necessary to provide optimum log response in a variety of
different logging environments. Control of source sub output
intensity is traditionally accomplished by varying the intensity of
an internal radioactive source. Because of the expense of a
radioactive source and the problems associated with radioactive
sources, it is problematic to have a large assortment of
radioactive sources of varying intensities or Isotopes to meet the
needs of varying logging environments. The major problems
associated with producing several different radioactive sources are
radiation safety, exposure, logistics, management, and hazardous
waste. Thus there is a need for a method and apparatus that enables
efficient alteration of the output radiation intensity from a
nuclear source sub.
SUMMARY OF THE INVENTION
The present invention provides a system for efficient alteration of
the output radiation intensity from a source sub for determining
the integrity of a gravel packing system by a memory logging tool.
The present invention provides a high resolution, memory logging
tool that directly evaluates the effectiveness of the gravel
packing operation by measuring changes in the bulk density of the
annular region of the gravel pack, wherein the measurements are not
affected by the presence of radioactive tracers. The present
invention alters nuclear radiation output intensity by adjusting
three separate parameters for the nuclear source sub. These three
parameters are .mu..sub.m, the mass alteration coefficient of the
material from which the source sub housing surrounding the nuclear
source is made; .rho., the bulk density of the source sub housing;
and t, the thickness of the source sub housing material. These
three parameters can be altered by changing source housings at the
surface or by issuing commands from a processor downhole to cause
an actuator to change the source output intensity or area of
investigation. The distance between the source and detector is also
adjustable to alter the area of investigation. The source sub
length can be adjusted while operating down hole to optimize
measurements and enable optimal measurement in a wellbore having
more than one geometry or condition at different depth
intervals.
The gravel packing system includes a screen disposed in an annulus
between the wellbore and a production tubing. A tubing, such as a
wash pipe, disposed in the production tubing provides a fluid path
from the surface to the screen. A fluid inflow port in the tubing
provides a return fluid path from the screen to the tubing and to
the surface. A memory logging tool carried by the washpipe is
located in the tubing below (downhole) of the screen. Slurry
containing gravel is pumped from the surface to the screen. The
fluid returns to the surface via the in port. The tool includes a
source of nuclear energy, gamma ray detector, a memory for storing
data and a battery pack. Upon the completion of the gravel pack
operations, the tubing with the memory logging tool is retrieved
from the well at a selected speed. The tool is activated to record
data as it passes across the screen. The data is stored in the
memory, which is downloaded when the tool is retrieved at the
surface to provide a log to determine the integrity of the gravel
packing of the screen.
The tool may be operated in a continuous mode by activating the
tool at the surface prior to deployment. Preferably, the tool is
set at a sleep or inactive mode at the surface and activated upon
the occurrence of a predefined condition. The tool may be activated
when the wellbore pressure reaches or exceeds a predetermined
threshold or by remotely activating it from surface or by providing
a preset time delay, or by sensing the movement. The tool may
include a plurality of collimated detectors, each obtaining data
corresponding a particular gravel pack zone of interest.
Examples of the more important features of the invention thus have
been summarized rather broadly in order that the detailed
description thereof that follows may be better understood, and in
order that the contributions to the art may be appreciated. There
are, of course, additional features of the invention that will be
described hereinafter and which will form the subject of the claims
appended thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
For detailed understanding of the present invention, references
should be made to the following detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, in which like elements have been given like numerals and
wherein:
FIG. 1 is a schematic diagram, showing a memory-logging tool
according to one embodiment of the invention disposed in a tubing
during a gravel packing operation.
FIG. 2 shows a schematic diagram of a memory logging tool utilizing
a plurality of collimated detectors according to an alternative
embodiment of the present invention.
FIG. 3 shows the present invention deployed on a slickline.
FIG. 4 shows the present invention deployed on an electric
wireline.
FIG. 5 shows the present invention deployed on a coiled tubing.
FIG. 6 illustrates the source housing and detectors in a preferred
embodiment.
FIG. 7 illustrates the variable diameter and thickness for the
source housing; and
FIG. 8 illustrates the actuator in a preferred embodiment for
varying the output intensity and area of investigation
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 shows a schematic diagram of the memory logging tool placed
in a wellbore during an exemplary gravel packing operation. FIG. 1
shows a wellbore 101 formed from a surface location 102 to a
desired depth. The wellbore 101 is lined with a casing 104 to a
shallow depth from the surface. A wellbore liner or casing 106 is
shown placed from the casing 104 along the length of the wellbore
101. Cement 103 is filled in the annulus 105 to set the liner 106
in the well to recover hydrocarbons from a subsurface
hydrocarbon-containing formation or reservoir, such as reservoir
110. Perforations 112 are made through the liner 106 and into the
formation 110 to allow the formation fluid to flow to the wellbore
101.
A production tubing 115 placed in the well acts as a conduit for
the flow of hydrocarbons 111 to the surface 102. One or more
screens, such as screen 114, are placed in the annulus 113 between
the perforations 112 and the production tubing 115. A packer 116 is
placed in the annulus between the casing 106 and the production
tubing 115 above or uphole of the screen 114, which packer prevents
the fluid flow through the annulus 113 above the packer 116. The
screen 114, which is usually a metal screen, is packed with gravel
to prevent flow of formation solids into the production tubing 115
and to reduce the velocity of the formation fluids entering the
production tubing 115.
In one gravel pack method, a tubing, such as a wash pipe 122, is
conveyed into a wellbore 101. A memory gamma ray tool 140 made
according to the present invention is attached inside the tubing
122 at a depth 142 which can be below or downhole of the screen
114. The tubing 122 includes an outflow port 123 that allows fluid
150 pumped under pressure from the surface to flow to the screen
114. A valve 124 opens when the pipe 122 moves. The tubing 122 has
a crossover tool (sliding sleeve) not shown, that allows the fluid
151 to flow from the screen 114 to the tubing 122, which is
returned to the surface via passages (not shown) provided
therefore.
Still referring to FIG. 1, the memory logging tool 140 includes a
nuclear source 130, such as a gamma ray source or a neutron source
to generate gamma rays or neutrons as the case may be into the
borehole. The tool 140 includes one or more spaced apart gamma ray
or neutron detectors 132, usually 6 to 24 inches apart. In the case
of a gamma ray source, gamma rays are emitted from the source 130,
which travel from the tool 140 to the screen 114 and into the
annular space 113. The spacing between the source 130 and the
scintillation detector(s) 132 is chosen so that the majority of the
gamma rays are scattered within a defined annulus with minimal
gamma rays penetrating the formation 110. The detectors 132 receive
the scattered gamma rays and provide a corresponding count rate. In
the above-described configuration, this count rate or volume is
proportional to the amount of scattering to which the gamma rays
are subjected in the defined annulus. The degree of scattering is a
result of the concentration or the bulk density of the sand or
proppant filling the annulus 113. The size of the gamma source 130
and detectors 132 are selected to produce a relatively large
density count rate wherein most of the counts are due to the energy
of the source 130 and a much smaller percentage of the counts are
due to isotopes (if any) injected into the formation 110. This
allows the use of the tool 140 to determine whether the annular
pack is of sufficient concentration that will prevent sand flowback
and whether the quality of the annular pack should be improved
through an intervention technique. The tool 140 further includes
detector electronics (electrical circuits and processors) 134 and a
memory section 136. Power to the tool electronic section and memory
section is provided by batteries in a battery section 138.
The detector 132 includes a detector such as a sodium iodide
crystal and a photo-multiplier tube that converts the light signals
(proportional to the received gamma rays by the crystal) to
electric signals. The electronic section 134 processes these
signals to determine the count rate and the energy level for such
counts. The data generated by the electronic section 134 is stored
in the memory 136 for downloading after the retrieval of the tool
140 to the surface.
To determine the effectiveness of the gravel pack operations, the
tubing 122 with the associated equipment (not shown) and the memory
logging tool 140 is located in the manner shown in FIG. 1, such
that the memory tool 140 is located below the screen 114. Slurry
150 containing gravel or sand is pumped by a pump 160 from a source
162. The pipe movement opens the valve 124, thereby allowing the
gravel slurry 150 to pass to the screen 114 via opening 124a. The
gravel is packed in the screen 114 and the fluid 150 substantially
without the gravel leaves the screen 114 and enters the tubing 122
via an inlet or inflow port 125. The fluid 151 returns to the
surface 101.
The gravel continues to pack the screen 114, which process can take
several hours. As the gravel packs, the pressure at the screen
continues to increase. The gravel pack operator sets parameters at
a predetermined pressure, above which it is presumed that the
gravel packing has been accomplished and the process is stopped. In
one embodiment, the memory logging tool 140 includes a pressure
switch or pressure sensor 137 which is preset to a pressure
threshold that is expected to be attained during the gravel packing
operations. When this pressure threshold is exceeded, the tool 140
enters a wake-up mode, calibrates itself and becomes ready for the
logging operation and starts to record data. Alternatively, a time
delay may be provided before the tool 140 is activated to record
data. The tool may also be set at the surface to continuously
record the data or it may be remotely-activated from the surface by
any suitable telemetry methods, including communicating control
signals to the tool 140 in the well 101 by acoustic pulses,
electromagnetic signals or pressure pulses. Accelerometer(s) may
also be installed in the tool 140, which activate the tool 140 upon
sensing tool movement due to the retrieval of the tubing 122 from
the wellbore 101. In any event the tool 140 is activated to record
data when the tubing 122 is retrieved from the well 101. When the
tool is moved out of the well, the accelerometer sensor signals may
be utilized to activate the tool.
At the conclusion of the gravel pack pipe operation, the tubing 122
is retrieved at a selected speed, thereby allowing the tool 140 to
traverse the entire length of the gravel-packed section at such
speed (the logging speed). The gamma ray log for the gravel-packed
section is recorded in the memory 136 of the tool 140. Upon
retrieval of the tool 140 from the well 101, the memory 136 is
downloaded and a wellsite plot of count versus depth obtained,
which provides the condition of the gravel pack and thus the
effectiveness of the gravel pack operation and the integrity of the
gravel-packed section. The logs may include count rate curves from
one or more of the detectors 132 scaled such that high pack density
and low pack density areas are relatively easily identified.
An important feature of the memory logging tool 140 is the ability
to run the tool 140 on a variety of hoisting mechanisms because the
tool 140 can be run on a coiled tubing, rope or chain, slickline,
wireline or any other suitable conveying device. Conventional
electric wireline, slickline or non-electric wireline, coiled
tubing and actual work siring or wash pipe (132) used in the gravel
pack procedure can be utilized to deploy the memory logging tool
140 into and out of the wellbore 101. Because of the high cost of
well intervention with the wireline tools, washpipe, such as 122
show in FIG. 1, is the preferred method of tool deployment. With
this method, as noted above, the bottom of the tool 140 is placed
inside the washpipe at or below the sump packer 163, which usually
is the lower most seal between the screen 114 and the casing 106.
The memory logging tool 140 with a finite amount of memory 136 and
available battery packs can be put into a "sleep" mode whereby the
major power consuming devices of the tool 140 are inactive during
gravel pack operations, thus saving battery power. The tool 140
does not record substantial amounts of data during the sleep mode,
thus preserving memory for the actual logging trip out of the
wellbore 101.
An additional benefit of the present invention is that the washpipe
tool transport mode requires no additional rig time as is required
by wireline trips. Rig time costs offshore can run tens of
thousands to hundreds of thousands of dollars per day. As noted
above, the present tool may also be operated in other modes,
including initializing the tool logging mode with a programmed time
delay, with an accelerometer which uses tool movement due to
retrieval of the tool 140 from the well 101 to activate the tool.
The tool may be operated continuously during trip into and out of
the wellbore.
FIG. 2 shows an alternative embodiment 200 of the memory logging
tool of the present invention. The tool 200 includes a gamma ray
source 210 and a plurality of collimated spaced-apart detectors.
FIG. 2 shows two such spaced-apart detectors 212a and 212b. Each
such detector may be arranged on the tool to evaluate a
proportional degree of the circumference of the sand control
screen. The tool 200 also includes a microprocessor-based control
circuit 230, a memory module 232 and a battery pack 234. A pressure
switch 236 may be provided to activate the tool as described above.
Other activation methods, as described above in reference to FIG.
1, may also be utilized.
The tool 200 can be azimuthally oriented such that the degree and
location of any imperfections or voids in the gravel pack can be
detected. The tool 200 may include two or more collimated detectors
with an orientation package referencing one of the detectors to the
high side of the tool in the wellbore. This is especially useful in
horizontal or deviated wells, thus, any imperfections or voids
sensed by the detectors can be located with reference to the high
or low side of the wellbore and can be quantified as a percent of
the circumference of the packed or unpacked areas.
FIG. 3 shows the present invention deployed on a slickline 315.
FIG. 4 shows the present invention deployed on an electric wireline
415. FIG. 5 shows the present invention deployed on a coiled tubing
515.
Thus, the present invention provides a self-contained, self-powered
memory logging tool for evaluating the integrity of gravel pack in
a wellbore annulus, wherein the tool is placed below the annulus to
be gravel packed prior to gravel packing the annulus and the tool
is retrieved subsequent to gravel packing to record logging data in
the tool memory, which data is downloaded at the surface to obtain
a log for determining the integrity of the gravel pack.
The present invention enables the variation of output radiation
intensity to optimize the log response in a variety of different
logging environments. The size of the wellbore or geometry of the
wellbore can change during a logging run. Moreover, the screen size
and casing size can vary during a logging run. The present
invention provides a method and apparatus to alter the output
intensity down hole during a run or uphole before a logging run by
changing the size of the nuclear source; changing the material from
which the sub source housing is made or by changing the thickness
of the sub source housing.
Turning now to FIG. 6, a schematic representation of the present
invention is illustrated. AS shown in FIG. 6, the present invention
resides in a tool comprising a battery 601, memory 602,
microprocessor 603, long spacing detector 604, short spacing
detector 605, gamma ray source 606, and gamma ray sub source
housing 607. The intensity of the gamma ray out put can be varied
by the present invention by changing the sub source housing 607. A
plurality of housing are provided having variable thickness 701 and
variable lengths 702, 702A. The output intensity changes as a
function of the thickness 701 of the material of which the source
housing is made. The thicker the material between the source and
the outside of the source housing, the less the intensity. The area
of investigation changes as the distance between the source and
detector changes.
The sub source housing 703 thickness or outside diameter 701 can be
larger than the greatest outside diameter as shown by dashed line
701A. The outside diameter 704 of the section of the source sub
housing above the source can be larger 704A to provide a borehole
excluder to force the gamma rays outside into the borehole wall in
an accurate path to prevent gamma rays from traveling directly from
the source to the detectors and avoiding the borehole wall area of
investigation.
FIGS. 7D and 7B show a cross section of the source sub housing a
nuclear source 606. Nuclear source 606 comprises a sealed
radioactive source 707 inside of a housing 708. The housing 708 is
made of different material known to have variable election density
and having a thickness 706.
As shown in FIG. 7B, the thickness 707 of the material is variable
and can be selected by choosing between a variety of different
housings provided by the present invention each having a different
outside diameter 701, inside diameter 708, thickness 707 and
material electron density. The housing can be made of titanium or
copper berillium to change the election density. Many materials
having different electron densities known in the art are
suitable.
Turning now to FIG. 8A, in a preferred embodiment a sleeve 801
having a plurality of materials 802, 803, 804 and 805 each having a
different election density or bulk density each having a different
effect on the radiation intensity emitted from the sub source
housing are moved along the longitudinal axis of the sub source
housing up 806 and down 807. The sleeve 801 is attached to an
actuator 808 which moves the sleeve. The actuator is preferably an
electromechanical device well known in the an for example, a ball
screw. The actuator 808 can also be a electromechanical e.g. ball
screw, hydraulic, e.g. moveable piston 810 known in art.
FIG. 8B shows a cross section of the actuator and variable election
density shield of FIG. 8A. In an alternative embodiment, the
nuclear source 606 is attached to rod 809 which is moved up 806 and
down 807 the longitudinal axis of the tool source sub housing
actuator 808. Varying the position of the nuclear source changes
the distance between the source and detector thereby enabling the
changing of the area of investigation while down hole during
logging.
By adjusting these three separate parameters, the source sub output
characteristics are adjusted to meet the requirements of the
logging environment without the need for multiple radioactive
sources.
These variables are based on the following equation:
I=I.sub.0e.sup.-t.mu..sup.m.sup..rho. I.sub.o=Original Source
Intensity I=Controlled Output Intensity t=thickness of material
between source and outer source sub housing (cm) .mu..sub.m=mass
attenuation coefficient of material (cm.sup.2/gm) .rho.=Bulk
density of material (gm/cm.sup.3) .mu..sub.m is a function of the
radiation source energy (MeV) and material electron density. "I" is
controlled by changing t, .mu..sub.m and .rho.. .mu..sub.m can be
controlled by changing the material(s) of the source sub
configuration. .rho. is controlled by changing the material(s) and
the bulk density of material(s) of the source sub
configuration.
The source sub can be made out of various materials having
different .mu..sub.m and .rho. properties in order to control the
output intensity. Combinations of materials can be used to obtain
the desired output intensity. Thickness of the source sub can be
used to control the output intensity. Multiple material layers
(cylinders) of different .mu..sub.m, .rho. and t can be combined to
control the output intensity.
The ability to change all material properties and thickness that
surround the source out to the outer surface of the source sub can
be used to control the output intensity.
Multiple cylinders can be incorporated in the source sub
configuration that can be introduced and removed from between the
source and the outer surface of the source sub to control the
output intensity. The material of movable cylinder(s) can vary with
distance allowing it to be moved along the sub axis until the
desired output intensity is accomplished. Shifting this layer while
downhole can provide the ability to gather more than one dataset
where the optimum configuration is not known or where wellbore
geometries or conditions vary across different depth intervals.
The source sub length between sources and detector can be changed
by changing subhousings to a housing having a different length
between the source and detector.
The source sub length can be adjusted to change the area of
investigation. The source sub length can be adjusted while
operating downhole to optimize the measurements. This enables more
than one configuration to be used to iteratively find the optimum
configuration. It also allows for optimal measurements in a
wellbore having more than one geometry or condition at different
depth intervals.
The foregoing description is directed to particular embodiments of
the present invention for the purpose of illustration and
explanation. It will be apparent, however, to one skilled in the
art that many modifications and changes to the embodiment set forth
above are possible without departing from the scope and the spirit
of the invention. It is intended that the following claims be
interpreted to embrace all such modifications and changes.
* * * * *